thumb|right|Silencer (silver) and [[exhaust pipe on a Ducati motorcycle]]

thumb|right|A silencer cut open to show the insulation, chambers and piping inside the shell

A muffler (North American and Australian English) or silencer (British English) is a device for reducing the noise emitted by the exhaust of an internal combustion engine—especially a noise-deadening device forming part of the exhaust system of an automobile.

Operation

thumb|right|A cutaway muffler showing the interior pipes and chambers which reduces noise

thumb|right|A muffler with pipes

thumb|right|Dual [[tailpipes attached to the muffler on a passenger car to reduce the sound produced]]

Mufflers are installed within the exhaust system of most internal combustion engines. Mufflers are engineered as an acoustic device to reduce the loudness of the sound pressure created by the engine by acoustic quieting. Sound reduction techniques used in mufflers include: reactive silencing, resistive silencing, absorptive silencing, and shell damping. The noise of the hot exhaust gas exiting the engine can be abated by a series of passages and chambers lined with roving fiberglass insulation and/or resonating chambers harmonically tuned to cause destructive interference, wherein opposite sound waves cancel each other out.

The operation of an internal combustion engine produces distinct pulses of exhaust gas that exit through the exhaust pipes and the muffler. For example, a four-cylinder engine will have four high-pressure pulses for each operating cycle, a six-cylinder engine will emit six high-pressure pulses, and so on. Higher backpressure can also help nitrous oxides (NOx) emission reduction in some engines.

When engine performance is the main concern, the exhaust pipes and muffler should be large enough to facilitate breathing as well as small enough to create a high exhaust flow.

Some aftermarket mufflers claim to increase engine output and/or reduce fuel consumption by slightly reduced back pressure. This usually entails less noise reduction (i.e., more noise). Greater muffler flow may increase engine power, but excess muffler flow capability provides no additional benefits and can be more expensive as well as being noisier.

The legality of altering a motor vehicle's original equipment exhaust system varies by jurisdiction; in many developed countries such as the United States, Canada, and Australia, such modifications are highly regulated or strictly prohibited.

thumb|right|A muffler on a large [[diesel engine|diesel-powered truck]]

See also

  • Noise control
  • Hush kit
  • Hush house
  • Soundproofing
  • Anechoic chamber
  • Vibration isolation
  • Shock absorber
  • Cushioning
  • Damped wave
  • Damping ratio
  • Detuner
  • Sound attenuator
  • Suppressor
  • List of auto parts

References

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fi:Pakoputkisto#Äänenvaimentimet